Effect of C/CO₂ molar ratio on CO₂ atmosphere fluidized preheating activation characteristics of semi-char

There are many fields involved in China’s industry, and the carbon reduction is urgent. Oxy-fuel combustion is the core process of carbon capture in combustion. Coupling fluidized preheating activation with industrial kilns oxy-fuel combustion is a new way to expand fuel adaptability and achieve carbon capture during combustion. This study uses a small-scale fluidized bed continuous feeding experimental platform to investigate the effect of C/CO₂ molar ratio (CC ratio) on the fluidized preheating activation characteristics of raw semi-char (RC) by adjusting the feeding rate at a temperature of 1 050 ℃ and CO₂ fluidized rate of 0.17 m/s. The gas composition and low calorific value are analyzed, and the CO₂ reduction ratio is calculated. The specific surface area, pore structure and carbon frame structure of fine particle activated semi-char (FC) and large particle activated semi-char (LC) are characterized. The reactivity of RC and FC is evaluated using a high-temperature tubular furnace thermobalance at 1 300 ℃. The results show that the use of fluidized preheating activation technology has achieved the resource utilization of CO₂ and produced rich-CO fuel gas. When the CC ratio increases from 1 to 4, the CO+H₂ volume fraction in the gas increases from 69.24% to 79.08%, and the highest CO volume fraction of 68.96%, the CO₂ volume fraction decreases from 29.48% to 20.13%, and the CO₂ reduction rate increases from 50.37% to 57.56%. The low calorific value of fuel gas increases from 8.69 MJ/m³ to 9.83 MJ/m³, which is 1.55−1.88 times higher than the low calorific value of the fuel gas produced by the project as described in the reference. The produced fuel gas in this study is conducive to the ignition and stable combustion of the kiln system. As the CC ratio increases, the specific surface area of FC and LC first increases and then decreases. The highest specific surface areas of FC and LC are 291.21 m²/g and 477.15 m²/g, respectively, which are 48 and 78 times higher than the RC. FC and LC have rich microporous structures, and the degree of graphitization decreases while the active sites increase. The microporous area accounts for 54.93%−68.42% of the specific surface area. In comparison, LC has a higher specific surface area and incremental pore volume mainly due to its longer residence time in the reactor, which promotes the development of pores and forms a large number of micropores. The reactivity index R_0.5 and the average mass reaction rate of FC obtained under different CC ratios are higher than the RC, which reveals the good reaction characteristics of FC. It can be predicted that FC will achieve an efficient conversion during the high-temperature gas-solid activated thermal fuel combustion process. This research proposes a new route of fluidized oxy-fuel preheating activation for carbon-based fuels coupled with oxy-fuel combustion of gas-solid activated fuel with high-temperature. The influence of CC ratio on the characteristics of semi-char at CO₂ atmosphere with fluidized preheating activation technology is obtained. The positive role of CO₂ as a carbon and oxygen carrier is revealed. The research results provide a data support for the application of fluidized preheating activation technology in the industrial kiln oxy-fuel combustion industry.